Three female students — ages 14, 15 and 16 — say they were repeatedly assaulted and groped by the boys for months at the Schlossstrasse Middle School in Salzburg, Austrian news agency Kronen Zeitung reported.

The victims only came forward after hundreds of women reported being sexually assaulted by migrants on New Year’s Eve in Cologne, Germany.

Police said the allegations at the school dated back to November. The female students said they were repeatedly assaulted and groped by the boys.

The assaults reportedly became more severe over time, escalating from verbal abuse to physical violence.

The 14-year-old said she was often hit by a 15-year-old Afghan boy. In one instance, the boy struck her so hard from behind that she smashed her head into the desk, Kronen Zeitung reported.

She was attacked again on Wednesday by the same boy, who smashed her against a locker so hard that the school headmistress called police. They took both students to the station for questioning and after hearing the allegations expanded their investigation.

Headmistress Eva Szalony said the allegations were a “complete shock.”

She said the boys had all come to Austria as unaccompanied minors from Syria and Afghanistan, and she believed they were happy and grateful to be allowed to live in Austria and be enrolled at the school.

She told Kronen Zeitung the boys “were integrating themselves well.”

Local school officials in Salzburg said the incidents are being taken dealt with very seriously and said they will appoint a coordinator to oversee all school-age asylum seekers and their teachers.